1. Field of the Invention
The present invention relates to a gastight ball valve for granules.
2. The Prior Art
For handling a polysilicon material which is deposited in a fluidized bed and is in the form of granules with grain sizes of approximately 200 xcexcm to 3 mm, shut-off devices are required to control the flow of granules. Pipelines which are lined with materials which prevent the silicon from becoming contaminated, such as for example quartz glass, silicon or ceramic, are used to remove the polysilicon granules from the fluidized-bed reactor. The flow of granules in vertical conveying sections is blocked by means of devices which are likewise lined with the abovementioned materials.
A device of this type is described, for example, in U.S. Pat. No. 5,205,998. These shut-off devices are generally insufficiently gastight, so that it is necessary to use combinations of the abovementioned shut-off devices and downstream gastight devices. However, the gastight devices must under no circumstances come into contact with solids, i.e. granules or other bulk materials, since otherwise the sealing surfaces are damaged and gas-tightness can no longer be ensured.
It is an object of the present invention to simplify the conveying of granular materials, such as for example granular polysilicon which has been deposited in a fluidized bed, and to provide a shut-off device which is able to interrupt a flow of granules and ensures gas-tightness between a supply pipeline and a discharge pipeline. Moreover, it should be easy to manufacture the shut-off device in any desired size.
The above object is achieved according to the present invention by means of a shut-off device 1 which can be fitted between a supply pipeline 2 and a discharge pipeline 3, in the form of a ball valve, comprising a housing 4, a housing flow passage with an inlet section 5 and an outlet section 6, a shut-off ball 7 with a shut-off ball flow passage 8, the shut-off ball 7 being mounted in the housing 4, if appropriate by means of two sealing rings 9, 10, and an actuating drive 11 for the shut-off ball 7, wherein the inlet section 5 is designed in such a manner that it reaches into the shut-off ball flow passage 8, which is designed in such a manner that, in the event of the ball valve closing through rotation of the shut-off ball 7, that part of the inlet section 5 which reaches into the shut-off ball flow passage 8 is accommodated in a slot in the shut-off ball.
In the shut-off device according to the invention, the upper seal 9 no longer has to fulfil a sealing function. It is used to fix the shut-off ball 7 in the interior of the housing 4. In principle, it is possible for the shut-off ball 7 to be fixed in the interior of the housing 4 by the housing itself or by the inert lining 14 without a seal. The sealing rings are therefore optional.
The shut-off ball 7 is preferably slotted at a 90xc2x0 angle. Hence that part of the inlet section 5 which reaches into the shut-off ball flow passage 8 can remain rigidly inside the ball body during the rotation of the ball.
Furthermore, the shut-off ball flow passage 8 is preferably designed in such a way that, in the event of wear to the ball valve through rotation of the shut-off ball 7, initially a cone of poured granular material in the shut-off ball flow passage 8 interrupts the flow of granules. This occurs without producing gas-tightness between inlet section 5 and outlet section 6. Thus the gas-tightness between inlet section 5 and outlet section 6 is only produced when the shut-off ball 7 rotates further.
In this case, the shut-off ball flow passage 8 is preferably designed in such a way that the flow of granules is shut off with the smallest possible rotation angle of the shut-off ball 7. At the same time the seal 10 covers the shut-off ball flow passage 8 and thus covers the gas flow in the direction of the discharge pipeline 3 as late as possible. This reliably prevents the seal 10 from being damaged by the granular material.
This is preferably achieved by selecting a suitable diameter of the shut-off ball flow passage. For this purpose, the shut-off ball flow passage diameter is selected to be as small as possible, in order to obtain the maximum possible distance to the cone of poured material, but large enough to allow unimpeded flow of bulk material. Furthermore, for this purpose chamfers 12, optionally 13 are preferably present in the shut-off ball flow passage 8 below the inlet section 5, and optionally at the exit into the outlet section 6.
The chamfer 12 in the shut-off ball flow passage 8 below the inlet section 5 is designed at an angle which is adapted to the bulk material. In this case, the angle is to be such that even with a small rotation angle of the ball the chamfer forms a 180xc2x0 angle with the cone of poured material and the flow of bulk material is interrupted. On the other hand it is impossible for any bulk material to become jammed in the gap between inlet cross section and the ball.
If the shut-off device is to be used, for example, for handling silicon granules, the chamfer is designed in such a manner that, for a rotation angle of the ball of 15xc2x0, it forms an angle of 30xc2x0 with the surface of the silicon granules, since silicon granules form a poured cone with a slope of approximately 30xc2x0. As soon as the granules form a cone with an angle of 30xc2x0 to the horizontal, the flow of granules stops. This is achieved with a very high level of reliability by the chamfer 12 which is preferably present.
The chamfer 13 at the exit into the outlet section 6 and the position of the seal 10 are preferably adapted to one another in such a manner that the rotation angle of the ball between closing-off the flow of granules and closing off the flow of gas is as large as possible.